The present invention is directed to an automatic manipulator, and more particularly to an improved drive mechanism for an automatic manipulator such as a sprue picker apparatus.
Automatic manipulators in general are required to quickly and reliably perform repeatable tasks. The manipulator must accurately position itself in order to repeatedly perform a task. In the case of a sprue picker apparatus, such apparatus are typically mounted on a fixed platen or, in the case of smaller machines, on the frame adjacent to the fixed platen of an injection mold. After a part has been molded, the injection mold opens and the sprue picker apparatus must quickly remove the molded part. High-speed performance of this task is very desirable in order to minimize the amount of time that the injection mold is open. Therefore, it is very important that any sprue picker apparatus be able to quickly and precisely perform repeatable movements.
Typically, automatic manipulators such as sprue picker apparatus have three axes of movement: horizontal, vertical, and rotary. FIG. 1 is a perspective view of a conventional sprue picker apparatus. A gripper 10 is movable along a vertical axis 15 and rotatable about a horizontal axis 20 in the direction shown by the arrow A. In addition, the gripper 10 and the vertical axis 15 are movable along the horizontal axis 20. In order to provide precise movement of the gripper 10, conventional sprue picker apparatus typically employ vertical twin guide rods 25 and horizontal twin guide rods 30. Such twin rod assemblies are difficult to align; thus, making it difficult to minimize friction along the total stroke of the gripper 10. In addition, the twin rod assemblies are heavy and therefore slow the gripper 10.
Another problem with conventional sprue picker apparatus is that for rotary movement of the gripper 10 about the horizontal axis 20, they are subject to backlash. The improved sprue picker apparatus uses a double rack and gear mechanism to eliminate backlash at the rotational end positions.
Moreover, to achieve accurate positioning, the twin rods (25, 30) must be sufficiently rigid. Rigid rods, however are heavy and lower the maximum velocity at which the gripper 10 can be moved. Because the gripper 10 cannot be moved quickly, an injection mold must be held open for a longer period of time in order to remove parts; thus reducing the efficiency of the mold.